body {
    font-family: Arial, sans-serif;
    background: #f3f4f6;
    margin: 0;
    padding: 0;
}

.container {
    background: #fff;
    max-width: 350px;
    margin: 50px auto;
    padding: 24px 16px;
    border-radius: 10px;
    box-shadow: 0 2px 12px rgba(0, 0, 0, 0.07);
}

h1 {
    margin-bottom: 20px;
    font-size: 1.6em;
    text-align: center;
}

label {
    display: block;
    margin: 12px 0 4px;
}

input[type="number"] {
    width: 100%;
    padding: 8px;
    margin-bottom: 10px;
    border-radius: 5px;
    border: 1px solid #ddd;
}

.tips {
    display: flex;
    gap: 8px;
    margin-bottom: 10px;
}

.tip-btn {
    flex: 1;
    padding: 8px 0;
    background: #e5e7eb;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: background 0.2s;
}

.tip-btn.active,
.tip-btn:hover {
    background: #38bdf8;
    color: #fff;
}

#customTip {
    flex: 1;
    padding: 8px;
}

#results {
    margin-top: 18px;
    background: #f1f5f9;
    padding: 12px;
    border-radius: 6px;
    transition: background 0.4s;
}

#results p {
    margin: 8px 0;
    font-size: 1.05em;
}